Regulation of Mitochondrial Calcium Transport by Caloric Restriction in Rat Kidney

Abstract

Caloric restriction (CR) in laboratory rodents prevents obesity, promotes healthy aging, and increases resilience against several pathological stimuli. At the mitochondrial level, protection promoted by CR in the brain and liver is related to higher calcium uptake rates and retention capacity, preventing Ca2+‐induced mitochondrial permeability transition. Dietary restriction has been demonstrated to increase kidney resistance against damaging stimuli such as ischemia/reperfusion, but if these effects are related to similar mitochondrial adaptations had not yet been uncovered. Here, we characterized changes in mitochondrial function in response to six months of CR in rats, measuring oxidative phosphorylation, redox balance and calcium homeostasis. CR promoted an increase in mitochondrial oxygen consumption rates under non‐phosphorylating (state 4) and uncoupled (state 3U) conditions. While CR prevents mitochondrial reactive oxygen species production in many tissues, in kidney we found that mitochondrial H2O2 release was enhanced in CR rats, although levels of carbonylated proteins and methionine sulfoxide were unchanged. Surprisingly, and opposite to the effects observed in brain and liver, mitochondria from CR animals are more prone to Ca2+‐induced mitochondrial permeability transition. CR mitochondria also displayed higher calcium uptake rates, which were not accompanied by changes in calcium efflux rates, nor related to altered inner mitochondrial membrane potentials, or the amounts of the Mitochondrial Calcium Uniporter (MCU). Instead, increased mitochondrial calcium uptake rates correlate with a loss of Mitochondrial Calcium Uptake 2 (MICU2), an MCU modulator, in CR kidneys. Interestingly, MICU2 is also modulated by CR in liver, suggesting it has a broader diet‐sensitive regulatory role determining mitochondrial calcium homeostasis. Together, our results remark the highly organ‐specific bioenergetic, redox, and ionic transport effects of CR. Specifically, we describe the regulation of the expression of MICU2, and its effects on mitochondrial calcium transport, as a novel and interesting aspect of the metabolic responses to dietary interventions.